As the digital camera becomes popular in recent years, many users are now taking digital photographs easily. In the year 1999, digital cameras of 5,850 thousand sets were shipped throughout the world. Also, the shipment of more than 10 million sets is estimated in 2000. Technically, the performance of the digital camera has remarkably been improved. A high-resolution type digital camera having even more than 3 million pixels has been put into the market.
Major advantages of the digital camera are; the photographed image can been seen instantly on the spot, a scene can be photographed repeatedly until the photographer feels satisfied, and development cost required for a film camera is not necessary. Accordingly, a user can take photographs easily as many times as the user desires. Most users want the digital camera can easy be handled to almost the same extent as they use a conventional film camera.
The digital camera is generally used in a following manner: first a user takes a digital photograph by a digital camera. The obtained image data can be confirmed using a monitor of a liquid crystal display, etc. included in the camera. Furthermore, the image data is stored into a storage medium (such as a fixed-mounted internal memory, or a removable semiconductor memory card called Compact Flash, Smart Media, etc.)
In general, the maximum number of photographs is limited by the capacity of a storage medium housed in the digital camera. When it is required to take more photographs, it is required for the user to erase the image that was once taken. Otherwise, in case the camera is configured so that the storage medium is exchangeable, the user replaces the storage medium with a spare medium being carried.
The stored image data is mainly for use in a personal computer (PC) or print out using a color printer after the user gets home. More specifically, the digital camera user, after getting home, transfers the image data to a hard disk or other storage medium such as a magnetic optical disk (MO), CD-R or floppy disk for use in the user's PC. Furthermore, using an application software (commercially sold, or attached to the digital camera product) in the PC, the images are processed for generating thumbnail pictures or enhancing image quality, or used for print out.
The digital camera is required to be compact in size and light in weight, as ordinarily required to the conventional film camera, so that the user can easily carry while travelling. There have been developed a variety of digital cameras, including the type either having an internal memory, a removable memory or a large capacity disk drive, etc.
When the digital camera has a drive for optical disks (DVD, MO, etc.) a relatively large amount of photographs can be taken making use of a large capacity storage medium. However, the digital camera that includes the disk drive mechanism becomes larger in size and heavier, which becomes a disadvantage in portability as compared to the conventional film camera.
On the other hand, in other type of the digital camera having no disk drive mechanism, semiconductor memory is mounted for storing image data. This enables to decrease the size and weight. As an example, the weight becomes 200 to 400 grams that comes to be nearly the same as the compact film camera.
However, the capacity of memories (Compact Flash, Smart Media, etc.) currently attached to the digital camera is normally within the range of 8 MB (megabytes) to 16 MB. Currently, the image data of the digital camera tends to be higher in resolution, reaching nearly 1 MB per picture in a high quality mode (with less data compression). In such cases, at most 10 photographs can be stored in one storage medium. Therefore, when the camera is constituted by fixed (not removable) storage medium, the user has to limit the number of photographs to take, or put up with a decreased image quality. It is inconvenient especially when the user wants to take a large amount of high quality photographs especially during travelling.
In case of the digital camera having a removable storage medium, the user will purchase an additional storage medium to carry with the camera, so that the user can take photographs without feeling any restriction about the capacity. Nevertheless, the semiconductor storage medium such as Compact Flash is still expensive (for example, the price of a Compact Flash card having the capacity of 128 MB is approximately 40 thousand in Japanese Yen). This may be equal to the price of the digital camera itself. Therefore, it is not easy to have a spare storage medium.
One way to override the problem of memory capacity in the digital camera is that the user carries another disk drive mechanism or small sized PC together with the camera in order to preserve the photographed images into the disk drive mechanism or the PC. This method is, however, troublesome because the portable PC or the disk drive mechanism weighs too much (on the order of 1 kilogram) to carry with the camera. In addition, such portable equipment is expensive to carry as a backup. For these reasons, it is difficult to provide the easiness in portability such as the conventional film camera to the digital camera.